Optoelectronic devices such as vertical cavity surface emitting lasers (VCSELs) covert electrical current into light that can be used in optical communication signals or for other uses. The currents in such devices generally must be confined to specific regions for efficient conversion that minimizes power consumption and maintains a desirable optical field profile. Accordingly, such devices generally have current blocking structures that confine current to the desired regions. These current-blocking structures can be formed using a variety of techniques such as implantation, lateral oxidation, and etching with or without subsequent re-growth. All of these techniques have difficulties and limitations.
Implantation for current confinement relies on damaging the crystal lattice of a material in the optoelectronic device to render the material non-conductive. The nature of ion implantation processes causes poor localization of the implanted region. As a result, the boundary between an implanted region and a non-implanted region is soft, which leads to current flow through mildly implanted regions. Additionally, the implant can introduce defects that eventually lead to device degradation.
Lateral oxidation for current confinement is currently the method of choice for high performance VCSELs. Lateral oxidation can achieve a very sharp current aperture that for small (<10 μm) devices results in much higher performance than implantation can achieve. However, the oxidation process typically changes a material with a high aluminum concentration into oxide of the same material and is therefore very disruptive to the crystal lattice. As a result, device degradation that can be traced to the oxidation is seen in VCSELs that use lateral oxidation for confinement.
Optoelectronic devices with etched features tend to provide poor performance unless a complicated and costly re-growth is performed. Further, for VCSELs, re-growth has so far been unable to provide the high performance found in other semiconductor diode lasers.
New current confinement techniques are sought to overcome the limitations of the known techniques used in optoelectronic devices.